This invention relates to an illuminating device for an electric part of the manually rotatable type such as a rotary switch.
An illuminating device for an electric part wherein a light source is located inside an operation panel and emits light to illuminate a light conducting member located around a knob is used, for example, for a carcarried electric part.
Preferably, an illuminating device for an electric part of the type mentioned is designed such that an entire face of a light conducting member is illuminated uniformly by the light from a light source. Appearance of a portion of an illuminated face of a light conducting member which is far lighter or far darker than the other portion must be avoided because it will make it difficult to read an indication on or around the light conducting member.
By the way, most of electric parts in which such an illuminating device as described above is incorporated are of such a construction that an operation shaft is located at the center of a knob as, for example, in a rotary switch. Since an electric part of the type just mentioned cannot have a light source located at the center of a knob, commonly a light source is mounted at a location displaced from an axis of the knob. Accordingly, there is a problem that an indicating portion of the electric part is not illuminated uniformly because the distance from a light source varies at different portions of a light conducting member.
To eliminate this, another illuminating device for an electric part has been proposed wherein a light reflecting paint is applied to a face of a wall of a particular member which surrounds a light conducting member such as a support member for supporting a light source thereon so that light reflected by the wall face may be transmitted to a portion of the light conducting member remote from the light source. However, while uniform illumination can be attained better than illumination by an illuminating device which does not use a light reflecting paint, the illuminating device still has a problem that a sufficient effect cannot be attained because it is difficult to control the reflected light. It is also a problem that, since it is necessary to assure light paths from the light source to the reflecting face and the light conducting member, the degree of freedom in designing is lowered and the device has a relatively large overall size.